The present invention relates to a lead frame and a semiconductor device.
A lead frame for a semiconductor device is used to mount a semiconductor element. After a semiconductor element is mounted on a lead frame, a semiconductor element is sealed with a sealing resin and integrating the semiconductor element with a lead frame. A semiconductor device is mounted on a substrates such as a printed wiring board or the like. A typical lead frame generally includes a die pad, onto which a semiconductor element is mounted, inner leads, which are electrically connected to electrodes of the semiconductor element through wire bonding, and outer leads, which serve as external connection terminals when mounting a semiconductor device onto a substrate. Such a lead frame is required to have a good bonding property with respect to the semiconductor element. Further, a bonding wire is required to have a good wire bonding property for connecting the semiconductor element to the inner leads, and the outer leads are required to have a good bonding property for bonding the semiconductor device to a mounting subject such as a substrate. Soldering is normally performed to mount a semiconductor device onto a substrate. Nowadays, widely used lead frames include solder films that are formed beforehand on the outer leads to improve the bonding property of the outer leads.
In contrast, lead frames that allow the mounting of semiconductor devices onto substrates without using solder films are also being used. For example, as shown in FIG. 15, a lead frame 50 includes a copper or copper alloy base material 51, a nickel plating layer 11A, which serves as a lowermost or substratum layer, a palladium plating layer 12A, and a gold plating layer 14A. The plating layers 11A, 12A and 14A are sequentially laminated on the copper or copper alloy base material 51 (refer to, for example, Japanese Laid-Open Patent Publication No. 4-115558 and International Publication No. WO2005/117112). The lead frame 50 of such a structure is referred to as a palladium pre-plated lead frame (Pd-PPF). In the lead frame 50, the gold plating layer 14A, which is formed as the uppermost layer, prevents oxidization of the lead frame and provides a good wire bonding property for a bonding wire (e.g., gold wire) that connects a semiconductor element to inner leads.